The present invention relates in general to control devices for controlling the movement of sheet like material, and in particular, to a new and useful control device for guiding edges or a centerline of a material web which moves over rollers utilizing a circuit which responds to actual position values as well as speed values for the material web to produce a signal for controlling a controlling element to properly align or reposition the material web.
While manufacturing and processing web-like or sheet-like materials, it is well known to employ control devices for exactly guiding the edges or the centerline of the material web or sheet. Controllers with hydraulically or electrically actuated correcting elements are used for this purpose, with the correcting elements being embodied by reels and/or control rollers. To obtain a control which is free from hunting, the device for measuring the position of the web must be provided in close proximity to the associated correcting element. This, however, is frequently impossible, for example in instances where the web of material is guided through a kiln that is heated to a high temperature, or through a wet region. In such instances, the position of the web must be determined at a location which is remote from the correcting element, and this as a rule, results in an undesirable hunting movement of the webs.
According to U.S. Pat. No. 3,568,904, such a hunting motion may be eliminated by timing the adjustment of the correcting elements, or adjusting them stepwise.
A similar situation arises if the correcting element cannot be built in because of the layout of the unit, or if for technological reasons the control must be provided in the preceding zone. In such instances, a second measuring device may be provided at the location where the accuracy in guidance is wanted, and the measuring device which is mounted close downstream of the correcting element is then adjusted stepwise, with the timing depending on the speed in the unit (U.S. Pat. No. 3,568,904).
It is disadvantageous in this timed prior art control that the correcting signal is not proportional to the run of the web, so that this run cannot be adjusted to an exact zero deviation.